Flashing discharge device



Maircl 2," 1954 FLASHING DISCHARGE DEVICE Filed Dec. l, 1949 Nitrogen Pressure Mlcrons Carl. Kenlrg,

c. KENTY 2,671,184

the pressure of Patented Mar. 2, 1954 2,671,184 FLASHING DISCHARGE DEVICE Carl Kenty, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of y New York Application December 1, 1949, Serial No. 130,463

7 Claims.

This invention relates generally to the discharge of electricity through gases and more vparticularly to a new type of gaseous discharge istic 2537 radiation. In the iiuorescent lamp, the 2537 radiation is converted by means of suitable phosphors into visible light which is utilized for illumination purposes.

My invention is concerned with a new type of lamp which contains the usual mixture of a rare gas and mercury vapor, and to which a small quantity of a molecular impurity has been added. I have found that such an addition of a small quantity of a molecular impurity produces remarkable changes in the current conducting characteristics of the discharge device and also in the character of its radiation. Among other elects, the current through the lamp becomes pulsed and the discharge becomes characterized by transverse striations.

Accordingly, it is an object of my invention to provide a new type of electric discharge device which may be utilized to provide a flashing light output.

Another object of my invention is to provide an electric discharge device which has the characteristic of drawing a pulsed current when a constant unidirectional voltage is applied to it. Yet another object of my invention' is to provide a generator of a particular voltage waveform as will be described herein.

Further objects and advantages of my invention will appear from the following description taken in conjunction with the accompanying drawings. The features of my invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a simplified schematic illustration of an electric discharge device and operating circuit therefor in accordance with my invention.

Fig. 2 is a curve illustrating the variation in the potential across the device as a function of a molecular gas therein.

Figs. 3,4, and 5 contain a number of curves illustrating graphically various operating characteristics of the discharge device of Fig. 1.

Fig. 6 is a schematic diagram of a circuit embodying the flashing discharge device as a source of a particular voltage waveform.

Referring to Fig. 1, there is shown an electric discharge device l, comprising an elongated glass tube 2 having sealed into one end thereof a thermionic cathode 3, and into the other end, an anode 4. Envelope 2 contains a rare gas such as l argon under a pressure of a few millimeters, and a small quantity of mercury so that the envelope is lled with the vapor of mercury at the pressure corresponding to the temperature at which the device is operated, this normally being room temperature. Device l may, for instance, be a glass tube 11/2 in diameter and 4 feet long.

The device is connected to operate on a suitable unidirectional voltage supply provided by 'a battery 5. Heating current for thermionic electrode 3 is provided by a small battery 6, and a resistor l serves as a ballast to limit the current through device I. For the discharge device which has been previously mentioned, battery 5 may provide a potential between 1,000 and 2,000 volts and ballast resistor l may be approximately 250,000 ohms. The description of the operating characteristics of the device which will now follow assumes that diierent devices containing variable percentages of gas mixtures are available or that means are provided for varying the gas contents of the device l herein.

When a pure rare gas such as argon, and mercury vapor are present within device l, and a discharge current not greater than 20 milliamperes and preferably in the range from 1 to 10 milliamperes is maintained, the arc occurs at a low voltage and contains the usual running striations. If now there is added a small quantity of a molecular gas which will not react chemically with the other elements in the device, such as, for instance, nitrogen (N2), the voltage drop across the device rises and the running striations are gradually suppressed. As more nitrogen is added, the pressure due to nitrogen being gradually increased from 0.1 to 20 microns for instance, the voltage across the device continues to rise to approximately 400 to 500 volts, as illustrated by curve 8 in Fig. 2. At a certain pressure of nitrogen, which, in the particular tube previously mentioned, occurs about 3.5 microns of nitrogen, the voltage drop or potential across the device suddenly decreases to an average value, perhaps 40 percent lower; and the discharge assumes a completely different form.

LI3QJTI4, filed- January 20, i950, entitled scope; and it is to `s'cription which now In this new form, the discharge flashes on and ori periodically; and the current shows a sharply peaked Waveform somewhat in the manner of a saw-toothed Wave, as illustrated by curve il in Fig. 3. The current through the device ialls oli steadily from a time ti, to nearly Zero at a time ts, then jumps suddenly to a sharp maximum at timev tf1 and proceedsy again to tall toward zero. The whole process is repetitive and may have a frequency in the range from 25 to 2,500 cycles per second, depending upon a number of circumstances.

I have found that there are various ways of controlling the frequency or"v flashing. The ire.- quency may be raised by increasing the value of ballast resistor l; this also decreases the degree of current modulation and raises the average voltage across the tube. The frequency also be raised by increasing the nitrogen content or, more strictly, the ratio of nitrogen to mercury vapor. Other means of raising irequency are increasing the current and decreasingthe pressure of' argon. The averageV current characteristics of the device under these conditions' show a strong positive current characteristic that is, it behaves as a positive resistance in which the greater the current, ther greater the voltage drop across the tube. Flashing is also favored by a high ratio of nitrogen to mercury vapor and by a lovv current.

general, the upper limit oi allowable current for the flashing to occur varies as the ratio oi nitrogen pressure to mercury pressure. For the tube which has been described, hashing may occur with currentsv ranging ironi- Opi to millia-mperes. This corresponds to a current density of 0.01 to-v 2.0 niilliamperes per separe centimeter, although it is to be understood that, t ith other sizes or diameters oi tubes, some deviations from proportionality are to be expected. Beyond 'this range of current densities, another form of discharge occurs which may be used for identifying the nature of the molecular` impurity. For instance nitrogen may be distinguished from carbon monoxide because in this range the Yformer produces a positive volt-ampere characteristic, Whereas the latter produces a negative volt-ampere characteristic. For a more complete description of the method, reference may be made to my copending application No. Method of Measuring Molecular impurities in Rare Gases, and assigned to the saine assignee as the present invention.

YThe character of the discharge may be determined by means of a rotating mirror or a-strobobe understood that the defollows is based upon an inspection throughthe assistance of such laboratory rdevices and is not necessarily visible to the nakedeye. At the beginning of the ash inthe .device and just before the occurrence of the peak in the current waveform, there spring into beingbright strations along the tube which are spaced apart by a distance of approximately a tube diameter. These striationshave sharp convex boundaries turned toward the cathode. This striations appear to be essentially stationary and of short duration and occur most brightly at time ts inY Fig. 3, during the period just preceding the sharplourrent peak at time t1.. These striations areiindicated by s in Fig. l, and. by S5 in Fig. e -which shows the variation in the intensity of the striations during a complete cycle. The intensity of the striations then decreases as indicated by s1, sz, and ss in Fig.V 4, these intensities corresponding to the times ti, t2, and t3, respectively, indicated in Fig. 3. By time tf., the striations have completely disappeared; the tube is then substantially dark until time tt, when a flash occurs, bright striations reappear, and the process repeats itself.

It is to be understood that whereas the striations are essentially stationary during any one dash through the tube, they do not recur at the same point along the tube at successive flashes. in other Words, a subsequent set oi striations is not in the identical location of a precedent set, so that if the flashes occur at a slow enough rate, the striations'appear to be shifting back and forth continuously along the longitudinal of the tube. lrlov-.teven the flashes ci light resulting from the continuous building up and wiping outv of thestriations can readily be seen with the naked eye if the repetition rate is inode low enough.

I Wil-.l novvprovide what I consider to be the scientijrc explanation oi the hashing phenomenon occurringwithi'n my discharge. device.. However, it. is to be understood that while I believe this explanation to. be true, I. do,y not wish to bound' by its accuracy or correctness.`

The flashing, discharge is due., apparently, to the strong excitation o the argon, in the, steep potential vdrops at the. heads of the striations. The potential distribution throughout the length of the tube at this moment is illustrated by curve p5 of Fig. 5.A There iollows. a rapid diffusion oi argon resonance radiation, and more particularly the side frequencies thereof, sometimes lshown as the Wings, throughout the spaces between the striationsand the concurrent formation therein of argon resonance-'and metastable atoms. It might be stated at this' point that a metastable state of an atom;v in accordance with the common understandingr is. one in which an electron of the atom is in. an orbit from which it does not inunediatelyreturn to its: normal unexcited state. However, in;` the.y metastable: state,` as also in the resonance state,;the; atom vis capable of ionizing another atom of which the ionization potential is less than the potential of the said states of the rst-mentioned atom. `lccordingly, since the metastable andresonance potentials. of the argon atoms are greater than the ionization potential of the mercury atoms, the; argon atoms in these states immediately ionizeY the mercury throughoutthe space between the striations. The ionization-ofl the mercury then produces a sudden large incr-'casein 'conductivity throughout. the space within the tube, so that the current through ythe tubencreasesfasindicated bycurve 9 in Fig. 3 at time ti, .and the voltage acrossl it decreases as a result of the ballast resistance in series between thetubeand the source ot potential. The ensuing discharge. is only partly self-sustaining, because it'depends'mainly on .the two. stage ionization of mercury. The upper metastable state of the mercury appears tobe destroyed by the nitrogen. The lower` metastable state of mercury however does not provide a process which is efficient enoughk to besch-maintaining at the lower` voltage gradient which immediately follows the discharge, as indicated by pi in Fig. 5. As a result, the mercury deionizes and the current falls gradually to a lesser value again. Thereafter thevoltageacross the tube gradually in- Cle-SESVDSLSSng successively through the stages indicated by p2, ligand vp4 injFig. 5. t, this level, theun-iorm voltage gradient through the tube becomes. unstable again and changes precipitously to the sharply stepped one indicated by p5, concurrently with the reformation of the striations indicated by ss.

The function of the molecular impurity, which may, for instance, be nitrogenKNz), carbon monoxide (CO), or hydrogen (H2) is to raise the voltage gradient per striation high enough, through the destruction of the upper metastable state of mercury, from which ordinarily, most of the ions are produced, that the rare gas will be strongly excited and its metastable and resonance atoms produced. The rare gas must also have the quality that its metastable and resonance atoms have a potential or energy content greater than the ionization potential of the mercury. If this is not the case, the rare gas will not be able to ionize the mercury and the device Will not operate; for instance, xenon will not do for a rare gas because its metastable potential is less than the ionization potential of mercury.

In the operation of my device as a source of flashing power, it is important that the current therethrough be maintained at relatively low If the current is allowed to rise much over 20 milliamperes in the particular tube which I have described, the molecular impurity will react chemically with other elements in the tube, or in other Words, it will clean up and the flashing will cease.

I have found that it is possible to obtain considerable modulated electrical power with this device. For instance, flashing may be obtained with a discharge current through the device of 10 milliamperes and a voltage drop of approximately 300 volts, which represents 3 watts of flashing power. For such high currents, the frequency will be rather high. The modulated power may be drawn oif from device I by means of either resistance or transformer coupling; and since the rise in the current waveform is very steep,

high surge voltages may be transformer coupling.

Referring to Fig. 6, I have therein shown a circuit for obtaining a voltage modulated similarly to the current flowing through device I. Device I is energized, source 5 in series with a ballast resistance '5. Inserted in series between cathode 3 of device I and the negative side of source 5, is a resistor ii,

obtained by means of which is coupled to the control electrode 9 of a triode amplifying are provided tions to tube tube Ill. Resistors II and I2 in the cathode and anode connec- IIl, and a continuous circuit provided through a suitable source of potential, as a tap point I3 in battery 5. A voltage of waveform similar to that illustrated by curve S' of Fig. 3 may then be obtained at the cathode output terminal I4, or a like voltage of reversed polarity at the anode output terminal I5. In an application such as the present one, device I might profitably be reduced in size and made in a more compact form, such as la coil or helix.

Other uses and applications of my flashing discharge device may be made. It is evidently not restricted to the creation of flashes of light, or to the generation of voltage waveforms as described herein by way of non-limitative example only. Moreover, while certain specific embodiments have been shown and described, it is to be understood that various modifications may be made without departing from the invention. Thus, whereas I have shown the Adevice herein operated on direct current, it may likewise be operated on alternating current and suitable thermionic electrodes provided for the different mode of as before, by the high potential operation. It will be appreciated that where the frequency of an alternating current source is substantially less than the frequency of the ashes, then the source is in effect unidirectional for periodssu-bstantially greater than the time interval required to develop the flashes or regions of unstable voltage gradient, and the mode of operation of the device during those periods is then essentially similar to what has been described. It is also possible to use cold cathodes, in which case, a higher anode voltage is required. The appended claims are, therefore intended to cover any such modifications coming within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. Apparatus charge, comprising an evacuated glass envelope having sealed into the ends thereof a pair of electrodes, said envelope containing an inert gas at a pressure of a few millimeters, a small quantity of mercury and a molecular gas chemically non-reactive with the other constituents within said envelope and at a pressure in the range from 0.1 to 20 microns, and a source of voltage and a ballasting impedance connected in series across said electrodes for developing, within said envelope, a current density of 0.01 to 2 milliamperes per centimeter square in order to establish localized regions of unstable voltage gradient therein, said source being unidirectional for periods substantially greater than the time interval required to develop said regions.

2. Apparatus for producing a flashing discharge, comprising an evacuated glass envelope having sealed into the ends thereof a pair of electrodes, said envelope containing an inert gas at a pressure of a few millimeters, said inert gas having a metastable state potential greater than the ionization potential of mercury, a small quantity of mercury, and a molecular gas chemically non-reactive with the other constituents within said envelope and at a pressure in the range from 0.1 to 20 microns, and a source of voltage and a ballasting impedance connected in series across said electrodes for developing, Within said envelope, a current density of 0.01 to 2 milliamperes per centimeter square in order to establish localized regions of unstable voltage gradient therein, said source y.being unidirectional for periods substantially greater than the time interval required to develop said regions.

3. Apparatus for producing a flashing discharge, comprising an evacuated glass envelope having sealed into the ends thereof a pair of electrodes, said envelope containing an inert gas at a pressureV of a few millimeters, said inert gas having a metastable state potential greater than the ionization potential of mercury, a small quantity of mercury, and a molecular gas in the range from 0.1 to 20 microns, said molecular gas being current density of 0.01 to 2 milliamperes per centimeter square in order to establish localized regions of unstable voltage gradient therein.

4. Apparatus for producing a flashing discharge, comprising an evacuated glass envelope having sealed into the ends thereof a pair of electrodes, said envelope containing an inert gas at a pressure of a few millimeters, said inert gas having a metastable state potential greater than for producing a flashing dis-A the ionization potent l of mercurma small. quan.- titpcrl mercury,l anda mcleculangas. in the range from 0.1 tomo. micronssaid molecular gas. beingcf ak type such thatl itfwill .notreact chemically kwith the otherl elements contained fvcithin said envelcpe, and a source ci: unidirectional current anda resistance. connected vin series :across said electrodes for developing, within said envelope, a current density of"0.0-1 to ZxniBiamperes per centimeter square in order toestablish an unstable steppedlvoltage gradient'of s uicient. intensity, within localized'V regions, zto. .produce metastabie atoms. of said. inertf. gas.

5. Apparatus for ;producing a dashing discharge, comprising an evacuated glass envelope having sealed .into the ends thereof a pair of elec.- trodes, said envelope containing argon at a pressure of a few millimeters, a small. quantity of mercury and nitrogen at a pressure in the range from 0.1 to2() microns, and a source of unidirectional current and a resistance connected in series across said electrodes for developing, With- `inrsaid envelope, a currentdensity of 0.01 to 2 milliamperes per centimeter square in order to establish an unstable vstepped voltage gradient of sufficient intensity, within localized regions, to produce. metastable argon atoms, but of insufflcient intensity to cause said nitrogen to clean up.

6. Apparatus for producing a pulsed voltage output comprising an evacuated glass envelope having sealed .into the ends thereof a pair of electrades, said envelope. containing argon at a pressure of a few millimeters, a small quantity of mercury and nitrogen at; a pressure in the. range from v0.1 to 20 microns, va source of unidirectional current. and a resistance. connected in series across said electrodes for develcpingivithin said envelope, an average current density of 9.01 to 2 milliamperes per centimeter square in order to establish an unstable stepped voltage gradient of sufficient intensity, within localized regions, to

nrocicice:metestableargon atoms, hut of insumcient intensity to cause. said'nitrogen to clean up, and means connected to said source for translating the modulations of said current` to corresponding voltage Waveform.

'1. Apparatus for producing a non-sinusoidal periodic current of generally sawtooth waveform from a source of unidirectional potential comprising an elongated, evacuated glass envelope having an anode electrode and a cathode electrode in opposite ends thereof, said envelope containing an inert gas at a pressure of a few millimeters, a small quantity of mercury and a molecular gas chemically non-reactive with the other constituents within said envelope and exerting a pressure within the range from 0.1 to 20 microns, and a source of unidirectional potential and a resistance connected in series circuit across said electrodes, the potential of said source and the proportions of the constituents within said envelope being such as to develop an average current density of 0.01 to 2 milliamperes per centimeter square thereby to cause the periodic development of localized regions of unstable voltage gradient within said envelope, whereby the current in said circuit is modulated to produce said waveform.

CARL KENTY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,965,585 Foulke July 10, 1934 1,970,223 Case Aug. 14, 1934 2,128,270 Spanner Aug. 30, 1938 2,325,597 Abernathy Aug. 10, 1943 2,419,902 Mager Apr. 29, 1947 2,473,642 Found June 21, 1949 2,482,421 Lemmers Sept. 20, 1949 2,266,619 Campbell Dec. 16, 1941 

